Japanese Geotechnical Society Special Publication The 15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering

The geotechnical issues of the damage caused by the great east disaster and reconstruction for the Tohoku region

Motoki Kazama i), Tadashi Kawai ii), Kim Jongkwan iii) and Tomohiro Mori iv)

i) Professor, Department of Civil and Environmental Engineering, Tohoku University, 6-6-06, Aoba Aramaki, Aoba-ku, 980- 8579, Japan. ii) Associate Professor, ditto. iii) Assistant Professor, ditto. iv) Associate Professor, Department of Civil and Environmental Engineering, Faculty of Engineering, Maebashi Institute of Technology, 460-1, Kamisadori-cho, Maebashi, Gunma 371-0816, Japan.

ABSTRACT

The 2011 Off the Pacific Coast of Tohoku Earthquake which occurred on March 11 caused serious damage to the infrastructural facilities in the eastern area of Japan due to the strong motion of the earthquake and the subsequent tsunami. This paper includes a brief outline of the earthquake damage to various facilities in relation to geotechnical engineering, and the main geotechnical engineering problems which have emerged after this disaster, including ground subsidence caused by crustal movement, the consolidation of soft clay and liquefaction, liquefaction induced damage to river levees and tailing dams, the geotechnical damage related to Tsunami impact, and disaster waste management.

Keywords: 2011 great east Japan disaster, reconstruction work, waste management, earthquake damage, geotechnical issue

1. INTRODUCTION shown in Figure 1. Comparing the movement just after the earthquake and those after three years, complex but The 2011 Off the Pacific Coast of Tohoku slight crustal movement was shown to have continued. Earthquake which occurred on March 11 resulted in serious damage to the infrastructural facilities in the Table 1 Crustal movement observed at the Tohoku district3). eastern area of Japan due to the strong motion of the earthquake and the subsequent tsunami. A brief outline City Horizontal Vertical of the earthquake damage to various facilities in relation movement (cm) movement (cm) to geotechnical engineering, and main geotechnical Just in Just in after after 3 after after 3 engineering problems which have emerged after this Pref. quake years quake years disaster are reported (Ref.1,2). Miyako 230 330 -35 -42

Yamada 273 376 -49 -53 wate

2 GROUND SUBSIDENCES I Kamaishi 340 445 -54 -46 Ohfunato 426 527 -75 -61 There are two main causes of ground subsidence. 420 523 -65 -48 i One is the crustal movement which occurred over a wide Yamoto 406 503 -50 -23 yag Rifu 323 421 -29 -16

area. The other is surface ground deformations, in Mi particular the liquefaction of sandy ground and the Watari 280 368 -22 -8 consolidation of soft clayey ground. Due to subsidence, the area of land under zero meter 2.1 Wide area subsidence due to crustal movement in the Sendai plain increased from 3 km2 to 16 km2. Once Wide area subsidence occurred due to crustal the under zero meter area was flooded, because natural movement in this earthquake (Ref.3). An eastwards drainage cannot be expected, an artificial pumping horizontal displacement of approximately 5.3 m and drainage system had to be used. The short term effects of about 1 m subsidence were observed at the Oshika the flooding of the low land area included the difficulty electronic survey point in City in Miyagi of carry out searches of missing people and delay in the prefecture. The Geospatial Information Authority (GSI) start of first stage restoration works. Furthermore, the of Japan has 1240 electronic survey points, one at every long term effect is that a very fragile area was produced, 20 km distance, which observe GPS satellite extremely prone to high flood tide damage and flooding. continuously. Several results are listed in Table 1, and Actually, later in 2011, coastal areas were damaged due the distribution of displacement presented by the GSI is http://doi.org/10.3208/jgssp.ATC1-3-02 1148 to a high tide disaster caused by a typhoon (see Photo 1). 2.2 Ground subsidence due to the liquefaction of The direct damage due to wide area subsidence sandy ground and the consolidation of clayey include port facilities now rendered useless and ground agriculture damage due to the high salinity of the soils. The liquefaction of surface sandy ground also caused In addition, the reconstruction of the sanitary drainage ground subsidence. Extensive area liquefaction resulted system in the low land area is necessary. Because energy in subsidence by as much as 50 cm in the Tokyo bay is required to operate the pumping system, the system is reclamation area. susceptible to energy outages that occur in times of crisis. In areas with soft clayey ground, it is possible that In terms of reconstruction and revival works, the area such subsidence will accelerate in the future. Figure 2 under zero meters should be decreased as much as shows the accumulated subsidence observed in low land possible by land fill. areas in Sendai City from 2001 to 2012. It is found that From a viewpoint of the relative difference between large subsidence occurred just after the earthquake. In land elevation and sea level, wide area subsidence can be addition to this, it can be seen that subsidence trend after regarded as a rise in the sea level. Ground subsidence the earthquake is larger than that before the earthquake. needs to be observed carefully over the long term, and This can be attributed to the disturbance of the skeleton the effects on human society need to be analyzed structure of the soft clayey due to cyclic shearing during thoroughly. The results should serve as a useful for the earthquake. overcoming the problems associated with rising sea level due to global warming.

Fig.2 Ground subsidence observed at low land (soft clayey ground) area in Sendai City from 2001 to 2012.

3 LIQUEFACTION DAMAGE 3.1 Liquefaction damage in Tokyo bay area Severe liquefaction damage occurred around Tokyo Bay reclamation area. From the view point of external seismic force, because seismic intensity observed at the Tokyo bay area was not so large (the maximum acceleration observed at the K-NET Urayasu was 157 Gal) the long duration of seismic motion is considered to have triggered the liquefaction rather than the amplitude Fig.1 Ground subsidence after 3years by the Geospatial of seismic motion. The feature of the liquefaction Information Authority of Japan3). damage was significant large amounts of boiling sand, as shown in Photo 2. The extensive area liquefaction and large amount of sand boiling deposits are identical to the liquefaction damage which occurred in Canterbury, New Zealand, in February 2011 even though those resulted from short duration seismic motion from an inland fault earthquake. Therefore, main cause of the large amount of sand boiling is considered to be the properties of the soil material, which includes a large fines fraction. Actually, the reclamation soils at Urayasu City were a fine silty sand containing over 50 % fines. It is known that the soil material at liquefied areas in Canterbury Photo 1 State of the flooded Ishinomaki City in Miyagi earthquake also contained a high fines fraction. The low prefecture after the high tide with the 2011.8 typhoon. permeability of fine sand contributes to maintaining the

1149 high excess pore water pressure and fluid state. It should 3.3 Liquefaction Countermeasure at Sendai airport be noted that the aftershock which occurred just 30 Sendai Airport was constructed as a beach airport on minutes after the main shock contributed to the damage a natural levee consisting of sand. The SPT for the stiff in Tokyo. sand deposit was over 20 in most places, and the possibility of liquefaction was thought to be low. Even so, liquefaction countermeasures (permeation solidified processing, the cross jetting method and the compaction grouting method) were carried out in the part indicated by a pink hatch on Figure 3 due to fear that liquefaction might occur in back filling soils in the underground structure neighborhood where the runway is crossed. The effectiveness of liquefaction countermeasure was confirmed because liquefaction damage was observed only in the non-countermeasure areas, according to the damage investigation of Sendai Airport. Photo 2 Large amount of boiling sand deposits due to An airport, however, cannot be used when only its liquefaction at Urayasu City, in Tokyo Bay reclamation area. runway is safe and capable of functioning. When just one

thing goes wrong, the function of the terminal building, Non-plastic fines silt is the most susceptible material the control function of the airport and the access function to seismic liquefaction because of the reason given to the airport aerial transport function cannot be 100 %. above. This points to the high liquefaction potential of Even though the main runway did not experience fatal young reclamation ground. It should be understood that damage due to the earthquake at Sendai Airport, the reducing the fines content of non-plastic silt does terminal building was flooded by the tsunami and thus contribute to improve liquefaction potential. We should deprived of its function. The relief role the airport was also pay attention to the origin of the ground; for expected to play in the case of the expected Miyagiken- example, whether the soil comes from natural deposits oki earthquake was not possible. It is hoped that a or artificial reclamation, such as hydraulic fill or other disaster prevention measure of both the hard and methods, impacts susceptibility to liquefaction. software is developed, one that is capable of restoring the 3.2 Liquefaction damage in Tohoku district function of the system as quickly as possible. The liquefaction damage in the Tohoku-district has At present, the trend is to pay attention to the concept not been subject to as much discussion as that in the of the BCP (Business Continuity Plan). This requires Tokyo Bay area. This is because much of the sand making assumptions about the degree of the accident in boiling caused by the liquefaction which occurred in the deciding a plan of an action. While this seems easy, it is coastal area was destroyed by the Tsunami which actually quite difficult. Finally, the facilities themselves followed the earthquake. The traces of sand boils cannot become earthquake-resistant, and, of when it comes to be used as evidence of the occurrence of liquefaction. the concept of business as usual, it all boils down to However, based on the many photographs and images being stubborn. When we have no choice, we simply taken of sand boils caused by liquefaction before the have to persevere. tsunami and the liquefaction that occurred during the aftershocks, liquefaction certainly occurred. Photo 3 shows the re-liquefaction at Onahama Port caused by the earthquake that occurred at Hama Dori in Fukushima prefecture on April 11.

Photo 3 Re-liquefaction evidence caused by 2011/4/11 aftershock at Onahama Port, Fukushima prefecture.(by Tohoku Fig.3 Liquefaction countermeasures to the runway of Sendai Regional Development Bureau, MLIT) airport and their efficiency (The Tohoku Construction Bureau).

1150 3.4 River levee damage due to liquefaction strength, the soil is susceptible to liquefaction. The cause of most of the river levee damage in inland (4) Soft foundation ground condition: Water from areas in the Tohoku district was liquefaction. Among the diffusion due rainwater tends to remain. various damage, there was some that requires particular For the above reasons, it is most important that attention. Photo 4 shows the overview of the damaged earthquake resistance is improved by reducing the river levee in the Naruse-river midstream area, where an degree of saturation of river levee material. Particular embankment collapsed completely and was torn apart attention needs to pay to the susceptibility to liquefaction like a strip of paper. Traces of liquefied river levee sandy of the lower part material of the embankment. earth material on the soft clayey soil foundation ground Furthermore, attention should be paid when there is a were found during an excavation investigation after the high degree of saturation condition due to capillary force event (see photo 4). Also, a penetration scar of the sand should be considered. pulse to the embankment upper part was observed, with a liquefied sand layer approximately 1 m thick. It is thought that the sandy earth material of the bank body liquefied, and that this material was under the saturated condition due to consolidation settlement in the foundation ground and was in a loose state due to stress relaxation.

Photo 5 Squeezed trace in the sandy earth material from liquefied zone by the excavation investigation.

Sandy Saturated material loose zone Ground water table

Subsidence due to consolidation of foundation ground Photo 4 Liquefaction damage of embankment at Shimo- Soft clayey soil foundation nakanome district in Naruse River by Tohoku construction bureau.

A similar case has been reported: river levee sandy Fig. 4 Attention points in check and verification of river levee soils built on peat ground liquefied during the 1993 resistance to earthquake. Kushiro-oki earthquake. At the time, the consensus was 3.5 Tailing dam damage that this was an atypical case; however, the mechanism A tailing dam was also damaged due to liquefaction. A involved should be considered the main mechanism of tailing dam bank located south of Kesennuma City broke, damage to river levees built on the soft foundations. and the liquefied slag flowed downstream (see Figure 5). From such a knowledge, the Ministry of Land, The flow state from the satellite image of 4/7 clearly Infrastructure and Transport listed up the following confirms this. Slag is residual soil characterized as points for checking and verification, as illustrated in Figure 4. (1) Embankment material is sandy soils: In case of significant damage caused by embankment material liquefaction, the materials were sandy soils with low plasticity. (2) Water level of the river levee interior: It is considered that the deformation is more pronounced when the saturated zone large. There is an example of a clear contrast between the water level in the river levee between the damaged area and the non-damaged area in the next section. (3) Quantity of consolidation settlement: The range of the loose saturated river levee body increases. A decline in the density and a decline in shear strength are Fig. 5 Fluidization failure of tailing dam deposits due to possible: in a state of reduced density and sheer seismic liquefaction, (Google earth image 2011/4/7).

1151 poorly graded fine silt which has adopted a mineral at a tsunami from infiltrating the Sendai plain, which mining site. Slag mixes with water, and is sent by a pump dramatically decreased the amount of damage to areas to an accumulated place. Because of the loose state and inland from it. Now, as a multiple protection policy poorly graded soils, the possibility of liquefaction is high. against tsunami damage, the use of a prefectural road Because the water is not separate from the soil, it travels with a padded embankment to provide protection against a long distance once it fluidizes. Such damage has been another tsunami event like this one is being considered. reported in the past from sites all over the world. It is However, from the perspective of foundation thought that the fluidization mechanism of slag differs engineering, the technical requirements required to from that of the liquefaction of clean sand. To avoid provide earth structures with tsunami-proof and erosion- fluidization failure, it is necessary to use solidification proof performance have never been investigated. measures when depositing the slag. Research needs to be done on this point and also on mitigation in cases where over flow occurs. 4 DAMAGE DUE TO TSUNAMI 4.1 Damage to Port and Coastal facilities Many ports and harbor structures were subjected to the seismic motion and the force of the subsequent tsunami. Generally speaking, breakwater damage is considered to be caused by the tsunami, and damage to quay wall structures is the result of seismic motion and liquefaction. The damage mechanism to the breakwaters located in the tsunami affected area were investigated, as shown in Fig.6. Research on the foundation design of breakwaters subjected to the overflow of tsunami wave is required. In the case of quay wall structures, research is required on the combined effects of seismic motion, Fig.7 Over 1.1 km of the right side embankment of Shin- liquefaction and the rapid draw down of the water level Kitakami-river was washed away by a tsunami. in front of the structure. 4.3 Erosion of soils around bridge and building foundations Tsunami damage to road facilities on National Route 45 where the Tohoku-district Pacific Ocean coastal area is tied to north and south was also significant. The main damage involved the washing away of a pier of a bridge and a beam. In terms of geotechnical damage to the road facilities, the soils filled behind the abutment in the bridge approach portion were eroded by the tsunami (Photo 6 left). Furthermore, there was significant scouring damage around the buildings (Photo 6 right).

Fig. 6 Failure mechanism of breakwater due to tsunami wave force.

4.2 Damage to river dike at river mouse area River mouth area in suffered extensive damage. In one example, over 1.1 km of the right side of embankment washed away in the Shin-Kitakami- Photo 6 river estuary, as shown in Figure 7. Plans need to be made Left: The soil behind the abutment of the road bridge was to rehabilitate the area which incurred tsunami damage by washed away at National Route 45, Nami-ita Bridge. Right: restoring the embankment in the estuary which do not Scouring around a building (Water Treatment Center, southern involve simply restoring the embankment to its former state. part of Miyagi Pref.) This also applies to the restoration of an elevated railroad along the coast. As mentioned earlier, the ground subsided 4.4 Damage to buildings due to tsunami due to crustal movement, and this should be taken into With regard to the damage to reinforced concrete consideration when making decisions about the buildings and a steel structure buildings in Tsunami infrastructure and the future plans of the community. affected areas, attention should be paid to the damage at In a totally different take on embankments, the Onagawa town in Miyagi prefecture. Figure 8 shows the Sendai east expressway embankment stopped the distance and the direction of building displacement. The

1152 distances and the directions vary considerably. This During the processing work, a huge amount of soils, involved many various foundation types, including including ash after incineration, soils included in the individual foundations, spread foundations and pile waste and tsunami deposition soils (see Photo 7), were supported foundations, as shown in Fig.8. In addition to generated. In order to make it possible to use such large this, the liquefaction that took place before the tsunami quantities of earth and sand as resources and to use them reduced the frictional resistance of the pile foundations. effectively, improvements in the field of earth material These example of damage require careful attention when management are required. From the perspective of considering the basic design for a refuge for future preservation of the geotechnical environment, this tsunami events. disaster has provided an opportunity to rethink and improve the framework of regular waste treatment. No.5: RC, individual No.2: RC, Onagawa Town Foundation engineering can make a significant Friction pile foundation contribution in this field. No.3 : RC, end-supported pile

No.4: RC, spread foundation

Photo 7 Tsunami deposit, in Higashi- City in Miyagi

No.1: S, end-supported pile pref. (left) and a rice field in Soma City in Fukushima pref.(right). The characteristics of the deposited soil from the tsunami change from area to area.

6 CONCLUSIONS The damage caused by the Great East Japan earthquake Fig. 8 Buiding damage due to Tunami at Onagawa Town. Five has highlighted many geotechnical issues, including RC and S structure buildings were tilted down and moved by the ground subsidence, liquefaction, geotechnical damage tsunami (ref.4). due to tsunami, and the geo-environmental problem. 5 GEOENVIRONMENTAL PROBLEMS Each of them is summarized in this paper. Rehabilitation work is ongoing and geotechnical engineers have much The earthquake resulted in a huge quantity of disaster to contribute. waste and tsunami deposition soils. The total amount of waste in the three most affected prefectures (Iwate, ACKNOWLEDGEMENTS Miyagi and Fukushima) was about 28 million ton, as shown in Fig.9. The processing works in Iwate and We would like to express our deep gratitude to all those Miyagi prefectures were finished by the end of March, who have provided valuable information, in particular 2014. However, in Fukushima prefecture, the work has the Tohoku Regional Development Bureau of MLIT. We not yet finished, because the waste is contaminated by also would like to thank all the individuals who have nuclear substance. contributed the restoration work and to request further support for the affected area.

REFERENCES 1) Kazama M. and Noda T. (2012.10): Damage statistics (Summary of the 2011 off the Pacific coast of Tohoku Earthquake damage), Soils and Foundations, Vol. 52 No.5,

780-792. http://dx.doi.org/10.1016/j.sandf.2012.11.003. 2) Kazama, M., Noda T., Mori T. and Kim J. (2012.6): Overview of the geotechnical damages and the technical problems posed after the 2011 off the pacific coast of Tohoku earthquake, Geotechnical Engineering Journal of the SEAGS & AGSSEA,

Vol. 43 No.2, 49-56. 3) Geospatial Information Authority of Japan: Table of Results of Ground Settlement Survey Using Various Measurement Points, www.gsi.go.jp/chibankansi/chikakukansi40005.html. 4) Scientific report on great east Japan disaster, The Tohoku Fig.9 Amount of disaster waste generated including tsunami branch joint committee on scientific research of the great east deposition soils and the location of debris processing site in Japan earthquake and tsunami disaster, 1200p. (in Japanese). Ishinomaki City, the largest treatment site in affected area.

1153